Wafer bonding (also called wafer fusion) techniques have been extensively practiced for different applications requiring different substrates. These techniques enable two different wafers to be bonded together, so that fabrication of highly lattice-mismatched and orientation-mismatched heterostructures become possible without generating threading dislocations. For example, wafer bonding techniques have been utilized to form silicon-on-oxide (SOI) substrate, and for bonding III–V materials with other materials.
The prior art wafer bonding techniques, however, do not provide for fabricating a hybrid substrate by integrating three or more different types of material on a common carrier substrate. It is desirable to have a system chip which includes mixed devices, such as laser diodes for external communication, rf or microwave high-power, high-frequency devices for transmitting and receiving data, and high density, low-power silicon devices for logic and memory.
As an example, GaN-based high-electron mobility transistors (HEMTs) are known to have high saturation velocity and enhanced mobility in nitride semiconductor heterostructures. Accordingly, they are suitable for high-power applications at microwave frequencies. These devices are typically built on a GaN on sapphire substrate or a SiC substrate.
On the other hand, optoelectronic devices are typically built on a substrate formed by III–V materials. For example, InGaAsP/InP edge-emitting lasers are usually fabricated using InP over a silicon substrate. The bonding process entails first depositing a p-type InP substrate and capping it with a p-type InGaAs film. Second, a n-type InP substrate is deposited over the film. The n-type InP substrate is then bonded to the silicon substrate. The bonded wafer is then annealed at 400 degrees Celsius.
In order to create a sophisticated system, for example, a system having GaN based high-electron mobility-transistors and optoelectronic devices to realize more applications, it is required to integrate such different devices on more than two different substrates. It is therefore required to provide a substrate having multiple materials, i.e., a hybrid substrate, where each material can be used for fabricating one or more different devices. For example, one material can be used for fabricating the GaN based high-electron mobility-transistors, another material can be used for fabricating the optoelectronic devices, and another material can be used for high-density, low-power Si-based devices.
Additionally, by providing a hybrid substrate, chips fabricated from different materials can be fabricated on the hybrid substrate. For example, a first part of the hybrid substrate can be used for fabricating a GaAs chip, a second part of the hybrid substrate can be used for fabricating a InP chip, and a third part of the hybrid substrate can be used for fabricating a silicon chip.